LAG: Access Previous Row
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A finance report compares each month's revenue with the month before. The first month has no previous value, so it shows NULL.
Write a query returning month, revenue and the previous month's revenue as prev_revenue, using LAG(), with the rows ordered by month.
Constraints
- Columns, in order:
month,revenue,prev_revenue - The first month's
prev_revenueis NULL - Rows ordered by
monthascending
Hints
Hint 1
LAG(column) OVER (ORDER BY ...) reads the value from the previous row.
Hint 2
Add a normal ORDER BY month at the end to order the output.
Keywords
db
SQL
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